The present invention relates generally to an appliance for cleaning articles, and more particularly to an appliance having a decision system that uses turbidity and temperature measurements to adjust the washing cycle of the appliance according to the level of soft of the articles to be washed, the rate of soil removal, and the temperature of the water used for washing.
Reducing the amount of energy consumption in appliances such as dishwashers or clothes washers, is a significant problem, in part because a large amount of energy is needed to heat incoming water. For example, dishwashers use energy from two distinct sources. One source is the water-heating energy (WHE) consumed by the hot water heater that supplies hot water to the dishwasher. The second source is the electrical energy used to run the dishwasher pump and a resistance heating element enclosed in the dishwasher. The resistance heating element boosts the water temperature during wash and dries the dishes after they are clean.
The Department of Energy (DOE) requires manufacturers to measure the mechanical energy consumed by the motor and heating element with a kilowatt-hour meter and the quantity of water used with a flow meter and timer. The total energy consumption per cycle is defined as EQU E=WHE+M, (1)
where WHE is the water heating energy used by the hot water heater to supply hot water to the dishwasher and M is the mechanical energy consumed by the motor and heating element, that is measured with the kilowatt-hour meter. Incoming 120 F. hot water is assumed to be provided from a 50 F. cold source with a constant volumetric specific heat (Cv) of EQU Cv=0.00240 kwh/gal-F. (2)
The "Normal" cycle of a typical dishwasher uses a volume (V) of water for an entire cycle of EQU V=9 gallons. (3)
The equation for Water Heating Energy (WHE) is EQU WHE=V Cv(T2-T1), (4)
where T.sub.2 is the temperature of the heated water and T.sub.1 is the temperature of the water from the cold source.
Therefore, the WHE for one cycle is EQU 9 gal.times.0.0024 kwh/gal-F.times.70F=1.512 kwh (5)
of water heating energy. The average mechanical energy consumption per cycle runs about 0.65 kwh. From Equation 1, the average total energy consumption for a "Normal" cycle is 2.16 kwh. Therefore, reducing the water heating energy by reducing the water consumption has a major impact on the overall energy consumption of the dishwasher.
Previous attempts to increase efficiency have ignored the preparation or condition of dishes going into the dishwasher. For example, a person using a conventional dishwasher may rinse the dishes before they are washed if there is any uncertainty whether the dishwasher will completely remove all the soils from the dishes. If the person uses 10 gallons of hot water to rinse the dishes and then runs an "efficient" 9 gallon cycle, then the same 9 gallon cycle is run whether the dishes are pre-rinsed by the user or not. An adaptive dishwasher responds to the heavy load soil if not pre-rinsed with the 9 gallons or possibly less. However, if the person using the adaptive dishwasher cleans the dishes before loading the dishwasher, the adaptive dishwasher will detect dishes that have been pre-rinsed and use a modified 6 gallon cycle lowering total water consumption to 16 gallons. However, the conventional dishwashers do not efficiently adjust the washing cycle to match a user's habits. Thus, water usage and wash time are not fully optimized.